1. Field of the Invention
The embodiments herein relate generally to the field of post chemical-mechanical polishing (post-CMP) cleaning operations. More specifically, the embodiments relate to a composition of cleaning solution employed in the post-tungsten CMP (post-W CMP) cleaning process.
2. Description of the Prior Art
Modern integrated circuit manufacturing relies on chemical mechanical polishing (CMP) processes to smooth the dielectric layers that are used between conducting metal layers as electrical insulation. The CMP technique is also widely used in a damascene type process to fabricate metal interconnects such as copper or tungsten lines, and metal plugs such as tungsten plugs that serve as electrical connectors between metal layers.
The CMP processes involve holding and rotating a thin, flat substrate including semiconductor material against a wetted polishing surface under controlled chemical, abrasives, pressure and temperature conditions. As the term is used herein, “semiconductor substrate” refers to any construction comprising the semiconductor material, including, but not limited to, bulk semiconductive materials, such as a semiconductive wafer, and semiconductive material layers (either alone or in assemblies comprising other materials). The polishing surface is generally a surface of a polish pad comprising a porous polymer, such as an elastomer, for example, polyurethane. A polishing slurry contains a polishing agent, such as alumina or silica, which is used as the abrasive material. In addition, the polishing slurry may contain selected chemicals which react with various surfaces of the substrate during processing. The combination of mechanical and chemical removal of material during polishing results in superior planarization of the surface.
The CMP processes, however, may leave contamination on the surfaces of the semiconductor substrate. This contamination may be comprised of abrasive particles from the polishing slurry, which may include alumina or silica, along with reactive chemicals added to the polishing slurry. In addition, the contamination may comprise reaction products of the polishing slurry and the polished surfaces. Small debris from the polishing pad also has a tendency to adhere to the surfaces of the semiconductor substrate during polishing. The contamination may be removed prior to subsequent processing of the semiconductor substrate in order to increase device reliability and to avoid the introduction of defects that reduce the manufacturing process yield. Thus, post-CMP cleaning solutions have been developed to clean the substrate surface of CMP residuum.
Often, after the tungsten CMP polish is completed, the resulting wafer has at least two distinct surfaces to be cleaned. For example, the majority of the wafer surface may be the dielectric cap surface, such as a silicon carbide surface or a silicon oxide surface, while the remainder may be the freshly polished surface of the tungsten plug or the interconnects. Both surfaces may be contaminated with residual slurry and/or polymer to be cleaned in the subsequent post-W CMP cleaning process. It is known to use a mixture of tetramethylammonium hydroxide (TMAH) and hydrofluoric acid (HF) in the post-W CMP cleaning process. However, such cleaning solution exhibits poor cleaning efficiency on the silicon carbide (SiCx) surface. The slurry residues and/or polymer residues, which can be identified by Real-time Defect Analysis (RDA), are frequently observed on the polished silicon carbide surface even after treatment by a known TMAH/HF mixture.
Therefore, advancements may be warranted in post-W CMP cleaning solutions to effectively remove the slurry residues and/or polymer residues from the silicon carbide surface or any polished dielectric surface having surface characteristics similar to the silicon carbide surface.